What happened
On 01 August 2018, a Piper PA-3im (registration C-FNCI) was performing a scheduled transit from Penticton Airport to Calgary/Springbank Airport following survey operations in British Columbia. The aircraft, operated by Aries Aviation International, was cruising at 15,000 feet with two occupants on board: the pilot and a survey technician.
While approximately 40 nautical miles southwest of the destination, air traffic control instructed the flight crew to descend to 13,000 feet and reduce speed to 150 knots. During this phase of flight, an imbalance occurred between the engines, with the right engine producing less power than the left. Shortly thereafter, at an altitude of roughly 13,500 feet, the aircraft lost controlled flight. The plane struck terrain near the summit of Mount Rae at 13:36 Mountain Daylight Time, causing a fire and an explosion upon impact. Both the pilot and the technician sustained two fatalities. Emergency signals were transmitted via an ELT, prompting a search and rescue response that reached the site within one hour.
Findings
Investigation into the accident identified several critical contributing factors. The primary cause was determined to be hypoxia-related cognitive impairment resulting from the pilot's failure to use supplemental oxygen while flying above 13,000 feet. This lack of oxygen likely prevented the pilot from recognizing physiological symptoms or managing the aircraft effectively.
As the aircraft entered a right-hand spin, several aerodynamic factors contributed to the loss of control:
- The airspeed dropped below both the stall speed and the minimum control speed.
- Significant power asymmetry existed between the engines.
- High angle of attack and drag from the windmilling right engine propeller.
While the pilot attempted a single recovery step by reducing power to idle, no further recovery procedures were completed. Investigators noted that while weather conditions like icing or turbulence were not factors, the pilot's inability to respond to the asymmetric power condition was a direct result of oxygen deprivation.